For what it's worth, here is a tentative build for a quiet PC. It will be used primarily for office applications, including voice recognition software, with some multitasking.

Case: P280
CPU: i7-3770
Mobo: ASUS P8H77-V
Ram: Kingston HyperX 12 GB DDR3-1600
HS: HR-02 Macho
HS fan: Noiseblocker S-Series M12-PS PWM
Internal fans and rear exhaust fans: Noiseblocker M12-S1
PSU: Cooler Master Silent Pro MII 520 W
Storage:
2x SSD Intel 330 120 GB
2x HDD Spinpoint F4 EcoGreen 2 TB (HD204UI)
All four connected to Lian-Li HDD power switch BZ-H06
Optical: ASUS BC-12B1ST (also connected to the Lian-Li switch)
OS 1: Windows 7 pro 64-Bit
OS 2: Windows 8 consumer preview 64-bit

No doubt the first critical reaction will be that this configuration is overkill, but note that memory-hogging applications will be used in addition to the usual office software.
H77 chipset because this is not an overclocked gaming PC.
P280 because of its cable management (HDD power switch, up to 6 cables) and other features such as front panel USB 3.0. The door is a pain in the derrière because of the Lian-Li switch, though.
P183 v.3 was my first choice, but front panel USB has to be re-routed over back panel. Solo II also appealing, but that piano black finish....
Unsure about some components, such as the Noiseblocker fans instead of usual Scythe, the Cooler Master PSU, and the i7 3770.
Asking myself what the best cooling concept would be in view of 4-5 storage devices but onboard graphics.
For SPCR reader responses, many thanks in advance before I tackle this build.

The Core 3770 only has a TDP of 77 W, so you could suffice with a Scythe Mugen 3. It will save you some money compared to the Thermalright HR-02 Macho since you won't need to buy another fan (the stock fan is great and can be run as low as 300 rpm). The CPU should also suffice with only a CPU heatsink + fan and a rear exhaust fan. This makes the two open top fan positions less desirable. Perhaps you could consider the Fractal R3 or R4, which is very similar to the Antec P183/P280. The Fractal Design Define Mini could save you some room being a mATX case with room for six 3,5" hard drives (soft mounted).

Why not go for 16 GB instead of 12 GB RAM?

The WD Green is more quiet than the Samsung F4 EcoGreen.
http://www.silentpcreview.com/article1127-page5.html

Can you spend a little extra money on the Seasonic X or a Kingwin PSU? These have been reviewed & approved by SPCR unlike the Cooler Master Silent Pro MII. I know, the Silent Pro M was decently quiet, but that doesn't guarantee that the Silent Pro M II will be quiet too.

I think that was it

Unless there an unusually small price difference where you're going to buy, getting an i7 over an i5 is a bit wasteful considering how very close they are to each other in performance with almost all kinds of software. The i5-3570K has the same integrated graphics core.

Do you really want that costly Lian-Li HDD power switch? It's not a good idea for SSD's and you shouldn't be able to hear the 5400 RPM drives, although there are others than the Samsung F4's that are a smidgeon quieter. Maybe look at the WD Reds that were recently reviewed here. (I like my own Samsung F4's though so they're not a bad choice, and the P280 will deal with their vibrations.)

The Intel 330 180GB SSD might be an option if you are getting two 120's for the sake getting extra performance space. The 180's are about the same at cost per gigabyte and perform a little bit better simply thanks to being bigger.

Many thanks, mkk and kuzzia, for your kind replies.

1) i5 vs. i7.

The i5 3570K had been my first choice. I was seduced by an enthusiast's fascination with speed and technology to consider the i7 3770, but, you are right, it makes as much sense in this build as it does to take a bath in a swimming pool.

"K" unlocked CPUs in an H77 motherboard (see http://communities.intel.com/thread/29119) seem problematic.

But perhaps the Z77 chipset would be a better choice, anyway. Underclocking instead of "S" or "T" versions for energy efficiency?

2) Lian-Li power switch.

I am already using the Lian-Li power switch in another build (Intel DH67BL, one SSD, three HDDs, two separately booted operating systems) and have been very pleased. Of course, the respective OS must be separately booted (all drives turned off except for the booting drive), but I have no problems mounting non-OS drives under Windows, turning them off and on (and the S-ATA optical drive as well) while the computer is running. This nicely partitions off Internet from work applications and ensures overall quietness and economical energy usage.

Of course, ASUS has UEFI, a different BIOS, and I want to install two SSDs--and that may pose some challenges. Whether the SSDs would suffer--TRIM, for example--is a question I cannot answer and one I hope you could. Making BIOS changes, if required, might resolve issues.

3) HR-02 vs. Mugen.

Mugen is said to be a fine choice for a quiet PC and it was my first choice as well. But I wanted to try out Noiseblocker fans throughout the build to improve the overall sound signature and the HR-02 design appealed to me.

Without a discrete GPU, I think you're right, I could get away with a HS fan and exhaust fan, especially if the four HDDs/SSDs are not switched on at the same time.

By the way, in another build, I had a bottom intake fan (Papst) and a Noctua HS and fan. I removed the exhaust fan experimentally and its removal had little or no effect on operating temps. Wonders of positive pressure. That was a minimalist office build, though.

4) 16 GB vs. 12 GB.

Many would say that 8 GB would be perfectly sufficient. However, RAM is relatively cheap and occasionally I work with several programs simultaneously, including Dragon Naturally Speaking, a notorious memory hog. So, it was a question of 12 or 16 GB and I decided to go with 12 GB because according to one study I read, 16 GB doesn't add that much more than 12 unless you are doing video rendering, etc.

5) I like Fractal but I also admire the Antec performance line and would like to try out one of their quality cases.

6) PSU.

The Seasonic X series fanless are interesting but you have to have adequate ventilation elsewhere, so in the end you may have to add extra fans, thus defeating the purpose. Note, too, that a PSU fan is also drawing air out of the case.

Honestly, I am not even sure what the best PSU would be in a rig like this one. Should I use higher wattage to ensure lower temps? And it is a guessing game with PSUs, especially since so much depends on the mainboard. My main candidates are Enermax, BeQuiet, and the above CoolerMaster.

Regarding the PSU...your stressed load power will be in the 120-140W DC range. There won't be a thermal issue with a passive PSU. But, if you want to get an active unit, there is the X560 (same guts plus fan). The BeQuiet Dark Power Pro 10 series is getting good reviews.

Testing the different fan setups for your system is the best way to find out the best fan setup. So if temps are fine with a bottom fan, and without a rear exhaust fan, then go for it.

Nexus also make some excellent (ultra quiet) PSU's. The Nexus Value 430W and the Nexus NX-5000 (530 W) are extremely quiet according to SPCR reviews. Both received the Editor's Choice, though the Value 430 W was demoted to just "Recommended".

You don't even have a dedicated GPU in your rig, a 400w Seasonic fanless would be OVERKILL.. go fanless, the seasonic is not even going to break a sweat let alone generate any heat !!! My 460W fanless barely gets warm in my system which is semi similar to yours plus a GTX 680 !!

I like the P280 too but do yourself a favour and check out the Corsair 550D, it's what I'd build with if I was chosing right now.

1000

Hey, thanks for all the advice from you guys, who are better versed in these matters than I am.
According to my calculations, the maximum load should not be more than 200W even if all hard drives/SSDs etc. are switched on, and they won't be if I install the Lian-Li power switch.
So, as suggested, the 400W Seasonic fanless, or an alternative in this range, should more than suffice. But since I want modular cabling, my choices in the 400W category are limited.
I would not use the fanless in the P280 because of the bottom mount. Here, the Solo II should be a better choice, as stated by Lawrence Lee (and much appreciated) in his fanless build article (http://www.silentpcreview.com/article1221-page3.html).
Moreover, I am wary of fanless, as stated above, and there is some buzz (no pun intended) on the Internet about Seasonic coil whine. That might have something to do with the choice of mainboard, though, used with the Seasonic.
Solo II or Fractal R4 or Mini might actually be the better choice for a case, or I could gut an older case I have sitting around, the ST-11, which has some critical deficits but is solidly built and very quiet.
I'm not entirely persuaded about the virtues of the Corsair Obsidian 550D case.
The P280 is for gaming/workstation rigs and is oversized for this rig. But I really like the P280 and it would be a pleasure to build in it, and it has potential for more sophisticated future rigs.
The P280 mini, which I guess will be on the market soon, would be more appropriate. Perhaps a temporary build in the ST-11 until the mini turns up?
There is, of course, no such thing as the perfect case and choice of components, and, as we know, perfectionism can be deadly. In the end, all I hope for is a no-BS, form-follows-function build that meets my technical and aesthetic criteria.
Building quiet PCs is an art as much as it is a science.

Isn't the Seasonic X 400 modular?

Yep. And I wouldn't worry about putting it in a 'bottom chamber' style case either, I have mine in a P183 and it's FINE.

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